Irrigation and Vector-Borne Diseases: A Case Study in Sri Lanka

Matrix I1 From direct observation of the irriga.
tion system and of agricultural practices, and from
other information, we identified (Fig. 4) the point
in the irrigation system (eg., reservoir, main canal,
etc.) and in the irrigation cycle (e.g., pre-irrigation,
land-preparation, etc.) where the various breeding:
places become an important hazard to health.
Matrix 111 thus completes the stepwise causeand-effect
analysis, which starts with identifying the
vector and ends with identifying the irrigation feature
that influences vector habitat. Although the
matrices still need more data from both irrigation
and entomology, they provide a framework for
further study of the linkage between irrigation and
Figure 4. Matrix I t Location of potential breeding places.
Pre- Land- Crop Vegetative Harvest post-
Irrigation Preparation Establishment Growth Irrigation
Reservoir Al, GI Al, GI Al, GI Al, GI Al, ti1 Al, GI
MaidBranch Canal F1 F3 F3 F3 F3 Fl
Buffer Reservoirs A2 AI:BI;CI AI;BI;CI A1;BI:CI AI:BI,CI A2
Distributary AI;CI;GI AI:Bl,2 Al;BL,2 AI;B1,2 AI;til;CI AI;GI,CI
Channel FI F3;EI F3;EI F3;EI FI FI
Field Channel CI:F1 BI;C1,2 BI;C1,2 Bl:CI,Z CI;FI CI;FI
Field Ditch F2 F2 F2
Field D1 D2,6 D3,4,6 D5.h Dh D1
Field Drainage F2 BI;F2 Bl;F2 Bl;F2
Natural stream EI;FI C3;E2 C3E2 C3;E2 CXE2 El
Domestic Environ. G2 G2 G2 G2 G2 G2
Natural Enwron. AI;B1,2 AAI;B1,2 AI;BI,2 AI:B1,2 AI:B1,2 A1:B1,2
CI CI CI CI CI CI
Matrix I1 thus indicates the relative importance
of the irrigation system as a whole for potential vec.
tor breeding in the area, and singles out those ele.
ments of the irrigation system that contribute mos:
to the breeding risk.
Matrix III. Matrir 111 establishes the relationshill
between the location of the breeding places ant1
those features of water management and irrigatiorl
engineering that cause their existence: hydrology,
design, construction, etc. (Fig. 5).
vector ecology under the specific environmental
conditions of Zone 2.
Irrigation Features Related
to Vector Habitat Creation
Matrix I11 directs attention to that feature of the
irrigation system, which, by an analysis of its
details, will prove to be the cause of a particular
type of breeding place. Even so, a general rule
Figure 5. Matrix I11 Relationship between breeding place and irrigation feature.
Hydrology Farm-Water Deslgn Construction Operation Maintenance
Management
Reservoir
MaidBranch Canal
Buffer Reservoirs
Distributary
Channel
Field Channel
Field Ditch
Field
Field Drainage
Natural stream
Domatic Enviran.
Natural Environ.
Al
A%Cl
AI:Bl
AI;BI
Bt
AI;C3;EI
QFI
AI;BI;CI
m
D1.6
F2
Gt A1 A1
F3 F1,3
Bl A1 A1
AI;EI Al$l,Z;Cl C1 B1;CI;FI
GI EI;FIQ F3
FI BI:Cl,Z;Fl BI;CI,Z;FI BI;CI
F2
F2
BI
C3;EI,2
G2
B2
BI;F2
C3;EI.Z
G2
B2
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